Chemically activated deposition consists in carrying out a chemical reaction in a chamber between gaseous reactants so that a product of the reaction is deposited on substrates which are to be covered, and others are removed from the chamber in gaseous form.
Such a reaction is activated by heating the substrates and the reactant gas or by setting up and maintaining an electric discharge through the gas. This has the effect of ionizing some of the gas molecules and of increasing the chemical activity of others.
Ionizing the gas in this way avoids heating the substrates to temperatures as high as 1000.degree. C. to 1200.degree. C. Depositing can then be carried out at ambient temperature or at a temperature of only 200.degree. C. to 300.degree. C.
The electric discharge can be set up and maintained by means of a high-frequency AC magnetic field created by a winding. This method is herein referred to as the "inductive" system.
A DC or high-frequency electric field can also be used which is set up between two high-tension polarized electrodes. This method is herein referred to as the "capacitative" system.
As far as concerns the chambers or reactors, it is known to use tubular reactors for both systems, but only the capacitative system is used with so-called "planar" reactors and in which the electrodes are made of parallel plates.
The method by which the reactant gas is inserted into such chambers has an important effect on the uniformity in thickness of layer deposited, on the layer depositing speed and on the quality of the deposited layer. It is important for the gases to be uniformly distributed in the vicinity of the substrates so as to produce uniform deposits of high quality and with reasonable speed.
In some known apparatus, gas distribution manifolds are ring-shaped, the diameter of the ring being equal to or slightly greater than that of a substrate-carrying electrode. The Manifolds are disposed parallel to said electrode and they have orifices through which the gases escape to be supplied to the substrates.
The gas manifolds can also be of tubular shape and have small holes in them or they can even be rectilinear, the substrates in this case moving past the manifolds.
Known chemical-depositing apparatus using gas-injection components such as have just been described, and in particular, plasma-generating electrodes of the usual type, are the seats of pressure gradients, of variations in gas concentration, and of non-uniform ionization. This causes poor-quality layers to be formed whose thickness is not uniform.
Further, such apparatus have low production capacity and manufacture thereof is difficult to transpose to an industrial scale.
Also, the cost of manufacturing them is relatively high.
Preferred embodiments of the present invention mitigate the drawbacks outlined hereinabove and provide an apparatus for chemically activated deposition in a plasma which apparatus allows excellent-quality uniform deposits to be made while being simple in structure and very reliable.